Fiber optic communication utilizes optical transmitters, optical receivers and optical fiber, among other components, to transmit light signals through the fiber. The transmitters and receivers are often integrated into a single component called a transceiver. Transmitters are light sources, such as lasers or light-emitting diodes. Receivers usually include a photo detector.
A signal being transmitted through a fiber optic system may suffer amplitude attenuation due to energy absorption, beam scattering and other processes during transmission. To compensate for such signal loss during transmission, optical amplification may be used to increase the amplitude of the signal leaving the transmitters or to increase the amplitude of a signal coming in to the receivers. An amplifier placed after the transmitter to boost an outgoing signal is often called a power amplifier, and an amplifier placed before the receiver to boost an incoming signal is often called a pre-amplifier. Passive optical amplifiers, such as erbium doped fiber amplifiers (EDFA), are often used for such amplification.
Doped fiber amplifiers typically include a length of optical fiber that has been doped with certain elements. Such amplifiers amplify a transmission signal when the doped fiber receives optical energy from a pump source. Such amplifiers produce amplification by stimulated emission—the dopants in the doped fiber are stimulated to a higher energy state by receiving pump power and may achieve a population inversion. As energy falls back to lower energy levels additional photons may be emitted. Usually the doped fiber responds most efficiently to one or more pumping wavelengths. In other words, the amplification imparted to the transmission signal may have a gain curve with one or more peaks corresponding to wavelengths specific to that amplifier. A pump source is often chosen based on the peak gain wavelength of the doped fiber amplifier.
Conventionally, the pump sources for the power amplifiers and pre-amplifiers are separate and individual. Thus, one separate pump source is used for the power amplifier, and one separate pump source is used for the pre-amplifier. Often, a pre-amplifier requires less pump power than a power amplifier, as the pre-amplifier is intended to produce less gain. The cost of the pump sources is often a significant part of the total cost of the amplifiers. For example, in a typical power amplifier or pre-amplifier, the cost for its associated pump source can be 60–80% of the total cost.
Both long distance and metro area telecommunications systems employ systems which include optical fiber, transceivers and amplifiers. However, metropolitan area networks (MANs) tend to have shorter distances between transceivers and are more cost sensitive than long distance telecommunications systems. As such, the considerable expense of multiple pump sources is relatively more significant for metropolitan area networks.